Space discharge device



March 9, 1948. w. C. BROWN SPACE DISCHARGE DEVICE 2 Sheets-Sheet 1 Filed June 7, 1945 INVENTTOR.

M WILLIAM C. BR

. TTY.

March 9, 1948. w. c. BROWN SPACE DISCHARGE DEVICE Filed June 7, 1943 2 Sheets-Sheet 2 INVENTOR. WILLIAM C, BROWN) ATTY.

Patented Mar. 9, 1948 l m V 2,437,240 SPACE DISCHARGE DEVICE William C. Brown, Watertown, Mass., assignor to Raytheon Manufacturing Company, Newton, Mass, a corporation of Delaware l Application June 7, 1943, Serial No. 490,110

3 Claims. (01150-4215) This invention relates to a magnetron, and more particularly to one which has a plurality of possible oscillating modes, each determined primarily by the geometry of the internal structureoi the magnetron. A device of this kind is intended to oscillate in a predetermined principal mode so as to generate the predetermined frequency. As described and claimed in the copending application of Percy L, Spencer, Serial No. 421,145, now Patent No. 2,417,789, certain spurious modes of oscillation were avoided by means of strapping wires interconnecting alternate anode arms of a multiple anode magnetron. However, in some cases it is undesirable or impractical to utilize such strapping wires.

'An object of this invention is to devise a magnetron in which the use of strapping wiresof the foregoing type are avoided but nevertheless in which the frequencies f the different modes at which the tube structure is resonantare separated by sufficiently great differences to increase the efiiciency of the tube substantially over those tubes which do not utilize either strapping conductors of the foregoing type or the principles of this invention.-

' Another object is to accomplish the foregoing by a structure which is simple to manufacture and assemble.

The foregoing and other objects of this invention will be-best understood from the following description of an exemplification thereof, reference being had to the accompanying drawings,

wherein:

Fig. 1 is. a transverse section of a magnetron embodying my invention; and

Fig. 2 is a cross-section taken approximately along line 22 of Fig, 1, with certain parts thereof brokenaway. a

. The magnetron illustrated in the drawings comprises a tubular envelope i made of a cylinder of conducting material, such as copper. The ends of the envelope are covered by caps 2 and 3 likewiseformed-of conducting material, such as copper, and hermetically soldered in place on the ends of the envelope I. The envelope i is formed with a central annular projection 4. A plurality of radial plates 5 are soldered in place along the inner surface of the projection 4. These plates may be stamped out of a sheet of highly-conductive copper. The inner ends of the plates 5 form anode faces which cooperate with a cathode 6 supported substantially centrally of said anode faces. The cathode 6 is preferably of the indirectly-heated oxide-coated thermionic type having an outer conducting cylinder l coated with an 2 l electron-emissive oxide layer 8, and having an internal heater 9, the end conductors Hi and H of which project from the opposite ends of the cathode structure 5. In order to support and insulate the heater from the cylinder 1, a pair of insulating plugs 12 and I3 are inserted in the opposite ends of the sleeve 1, The. end conductors Hi and II pass through openings in these insulating lugs. A pair of conducting straps [4' are welded to the upper end of the sleeve I, extend across the outer surface of the insulating plug l2, and'are in turn welded to the end conductor In. This retains the end conductor l0 and the heater 9 in place, and also electrically connects the end conductor ill to the sleeve 1'. The lower insu- 'lating plug is retained in place by a pair of strips i5 welded in place at the lower end of the conducting sleeve 1. These strips, however, do not come into electrical contact with the end conductor H which is thus insulated from the sleeve 1. l

The cathode is supported and provided with external electrical connections by means of a pair of cathode and heater lead-in conductors l8 and Il. The conductor I6 is rigidly and electrically connected to the end conductor l0, while the conductor I! is rigidly and electrically connected to theend conductor H. The lead-ins I6 and I! are sealed respectively through glass seals [8 and 59 mounted at the outer end of conducting pipes 20 and 2i hermetically fastened through the wall of the envelope l adjacent the upper and lower ends thereof.

When such a magnetron is placed. between suitable magnetic poles 22 and 23 to create a longitudinal magnetic field and the device is energized. oscillations are set up. These oscillations may be led out from the tube by means of a coupling loop 24 extending into the space between two of the plates 5. One end of the coupling loop 24 is connected to the inner end of a conducting pipe 25 hermetically sealed through the wallof the envelope l substantially midway between the ends thereof. The other'end of the coupling loop 24 is connected to a conductor 26 which passes through said pipe 25 and is sealed through a glass seal 21 mounted at the outer end of said pipe. An additional conducting pipe, not shown, may be electrically connected to the pipe 25 and form with the conductor 26 a concentric line through which the high frequency oscillations generated by the magnetron may be conducted to a suitable utilization circuit.

Each pair of anode arms 5, together with the portion of the projection 4 between them, forms an oscillating cavity. A capacitance exists between the cathode E and the end faces of the anode arms 5. Also capacitances exist between the side walls of each oscillating cavity. The conductive path around each cavity afforded by the side walls thereof constitutes an inductance. The anode therefor is so designed and spaced relat ive to the cathode that the inductances and capacitances described constitute tuned circuits. It is desired that these circuits shall be resonant at a definite predetermined frequency at which the device is to be operated. The device is intended to operate so that each oscillating cavity is tuned to the frequency at which each of the other oscillating cavities oscillates.

In tubes of this type, the frequencies, at which the structure is resonant can be determined by feeding the output of an oscillator whose frequency can be varied into the oscillating cavities. The different frequencies at which the structure is resonant whioh are thus determined are designated as cold resonance frequencies of the tube. The more widely separated these cold resonance frequencies are, the more efficient is the tube due probably to the fact, that. there is less inclination for the tube to operate in two oscillating modes at the same time. I have found thatthe separa tion between such cold resonance frequencies can be increased substantially by the construction to be described below. Adjacent the end faces of the anode arms 51, at the upper and lower ends thereof respectively, are. supported a pairof con ducting rings 28 and, 29. These rings are conveniently formed by the outside of a pair of trough-shaped annular members 32 and Si, the inner wall of which is Welded to the surface of the. cathode. sleeve 1.. In this way the rings 28 and 29 are electrically connected to the cathode l, and are held sufiiciently close to the surfaces of the end faces of the anode arms 5 to be effectively coupled to said faces by the capacity which is thus produced between these members.

I have found that with. such an arrangement, the overall efiiciency of the tube is substantially increased. I believev this is due to the fact that the rings 28v and 29 each forms a path which has a. relatively low impedance to the desired oscil1ations, generated by the tube, and that these low impedance paths are coupled between the active anode faces. This facilitates the feeding of energy between successive oscillating anode loops, and reinforces the principal oscillating mode, while at the same time presenting an obstacle to the building up of spurious oscillating voltages. I have found that. in order to perform these functions, the rings 28 and 29 must be of substantial width in order to secure the requisite value of capacity coupling to the anode faces. Also these rings must be. placed sufiicient'ly close to the anode faces to. secure such value of capacity coupling. I have found, for example, in a particular embodiment of my invention, that rings having a widthof .055 inch and spaced about .020 inch from. the anode faces produced a highly satisfactory operation. Of course the actual values for these dimensions will vary with different geometrical arrangements and dimensions of the tube.

Of course it is to be understood that this invention is not limited to the particular details as describedabove inasmuch as many equivalents will suggest themselves to those skilled in the art. For example, instead of a pair of rings. coupled to the anode faces, in some cases it may be possible'to use a single ring. Also the portion of the active anode faces to which these rings may be coupled may be varied. It is believed that various other variations of structure in which the teachings of my present invention may be incorporated will suggest themselves to those skilled in the art.

What is claimed is:

1. An electron discharge device comprising a cathode and an anode having a plurality of electron-receiving face portions adjacent said cathode With a cavity resonator between each pair of electron-receiving portions, and a trough-shaped electrical conductor connected to said cathode,v said conductor having an arm of relatively extended surface area supported closely adjacent to and substantially parallel with said electron-receiving face portions.

2. A magnetron comprising a cathode and an anode having a plurality of electron-receiving face portions adjacent said cathode with a cavity resonator between each pair of electron-receiving portions, means adjacent said cathode for producing a magnetic field about said cathode, and a trough-shaped electrical conductor connected to. said cathode and having an arm of relatively extended surface area supported closely adjacent to and substantially parallel with said electronreceiving face portions.

3. An electron discharge device comprising a cathode, an anode in juxtaposition to said cathode, said anode having a plurality of electronreceiving portions, and a trough-shaped conductor having an arm connected to said cathode, and another arm closely adjacent to and. substantially parallel with said electron-receiving portions.

WILLIAM C. BROWN.

REFERENCES CKTED The following references are of record in the file of this patent:

UNITED STATES PATENTS Great Britain July 11, 1 939 

